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Using BS3871 MCB to protect ne submain

Alan B

Is it ok to connect a new submain to an existing spare 3 phase BS3871 MCB in a light industrial installation. The alternative is to change the entire main DB.

Submain will be clipped direct to wall and steel roof beam. It will feed a new 3 phase DB, probably equipped with two 3 phase 16A MCB's.

My understanding is that BS 60898 replaced BS3871 and the standards are similar, I am sure there are some differences, but do they make a significant impact on safety? In my mind providing they disconnect in the required time everything should be acceptable? Main risks will be after the sub board using modern devices.

Thanks

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    gkenyon said:
    So, it's clear that "back in the day" these products may well have been considered OK for providing isolation ... but they definitely don't meet the requirements for isolation of BS EN 61140 today (5 kV impulse withstand for CAT III, typically 3 mm gap

    So the myth buster in BPG 4 alluded to by AMK is wrong! The devices do not comply with 531.1.1 and, in any event, should not be used to isolate a circuit for electrical maintenance. 
    To be honest, I always took the same view as BPG 4 and would not mention any issues in reporting documentation even where the devices proliferate in the older installations, but I think I will review that, given the comments by the guru of electrical compliance.

  • 0 in reply to lyledunn
    lyledunn said:
    The devices do not comply with 531.1.1 and, in any event, should not be used to isolate a circuit for electrical maintenance. 

    I would prefer to say "The devices might not comply with 531.1.1 ..."

    On reflection, I ought to have said

    So, it's clear that "back in the day" these products may well have been considered OK for providing isolation ... but they definitely don't might not meet the requirements for isolation of BS EN 61140 today (5 kV impulse withstand for CAT III, typically 3 mm gap)

    There's every possibility that an older device may well have been designed such that it would pass tests and inspections of current standards ... but we do know it is highly unlikely to have actually been tested to the requirements of newer standards.

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  • 0 in reply to lyledunn
    lyledunn said:
    The devices do not comply with 531.1.1 and, in any event, should not be used to isolate a circuit for electrical maintenance. 

    I would prefer to say "The devices might not comply with 531.1.1 ..."

    On reflection, I ought to have said

    So, it's clear that "back in the day" these products may well have been considered OK for providing isolation ... but they definitely don't might not meet the requirements for isolation of BS EN 61140 today (5 kV impulse withstand for CAT III, typically 3 mm gap)

    There's every possibility that an older device may well have been designed such that it would pass tests and inspections of current standards ... but we do know it is highly unlikely to have actually been tested to the requirements of newer standards.

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